Hollow ceramic microspheres are hollow inorganic non-metallic spheres in small size, with a particle diameter ranging from 0.01 to 1.0 mm. They have the advantages of light weight, low heat conductivity, sound insulation, wear resistance, high dispersion, good electric insulation and good heat stability, with low manufacture cost, being novel light materials having light weight, high strength, and excellent properties with diversified uses. They can meet the requirements of petroleum cementing, automobile chassis shock-resistance, hull deck, fillers for organics including resins etc, emulsion explosive, high-quality fire-resistant coating, heat insulating refractory material, building interlayer heat insulation, sound absorption and noise taming, heat insulation and energy saving of building exterior wall, regression reflection materials, carriers of release-controlled drugs in biological pharmaceutical preparation, and can also be potentially used as light packaging materials of electronic industry, wave absorption materials, deep water floatation materials, low density adhesives, light weight and high strength concretes. As compared to traditional hollow glass microspheres, the hollow ceramic microspheres have higher compressive strength, which can be tens of times higher than the former one.
In the preparing of artificial marbles, hollow ceramic microspheres are used to reduce the weight of articles and improve the anti-cracking ability of articles. Hollow ceramic microspheres are used to manufacture synthetic woods, with the products having the same visual sense, appearance and structure as woods. They are mainly used for the fabrication of high-quality furniture, sanitary ware, furniture casts, and decorative boards et al.
Hollow ceramic microspheres are used as composite materials for repairing. The typical application is that hollow glass microspheres are added to resins to replace part of the fillers like calcium carbonate, talcum powder, etc, to prepare lime putty (putty). This novel lime putty has the advantages of light weight, strong adhesion, easy application, low shrinkage, and short curing time, particularly significantly improving the performance of foundry milling and polishing properties. They have been widely used in the repairing of various vehicles, shipping, and machine tools.
Hollow ceramic microspheres can be hollow spheres containing an amount of gases inside, with low thermal conductivity. Thus, hollow glass microspheres have the features of sound insulation and heat insulation, and therefore are good fillers of various heat insulating materials and sound insulating materials. Meanwhile, the hollow ceramic microspheres have been widely used in heat insulation materials.
Besides, hollow ceramic microspheres are also excellent sensitizers of emulsion explosives, can improve the sensitivity of emulsion explosives and prolonging the shelf time of explosives.
Existing hollow ceramic microspheres particularly mean hollow microspheres or hollow floating beads consisting of silicon dioxide (SiO2) and aluminum oxide (Al2O3), which are obtained by grading process, e.g. flotation, from fly ash or coal gangue. The hollow ceramic microspheres are actually micro- or sub-micro-size glass microspheres having a hollow structure and a shell of aluminosilicate glass, and are widely used in inks, binders, engineering plastics, modified rubbers, electrical appliance insulators. However, hollow ceramic microspheres other than aluminosilicates glass are difficult to be similarly prepared by this process at present.
Additionally, researchers have prepared hollow microspheres of other materials, such as TiO2 (Zhang Junling, et al, CN101580275A), ZnO (Xu Zhibing et al, CN1807254A), CdS (Xie Rongguo, et al, CN1559911A), Fe3O4 (Nie Zuoren, et al., CN101475223A), SiO2 (Yin Hengbo, et al., CN101559951A). However, these methods are restricted by the process and basically limited to prepare hollow microspheres with specific composition that can be obtained by solution chemical process, but difficult to be used for the preparation of hollow microspheres other than those with specific components.
The applicant has successfully prepared hollow microspheres of varies materials such as Al2O3, ZrO2, Si3N4, SiC, coal gangue, fly ash, WC, Ni etc, by preparing stable foam slurry and using centrifugal atomization process. One of the key steps used in the process is centrifugal atomization. Centrifugal atomization is one of commonly used atomization techniques. This process results in greater cooling rate than gas atomization process. At present, centrifugal atomization process is used to produce metal powders or rapid-solidified alloy powders, in which process, the metal is heated and melted, and spinned-out and crushed into droplets under centrifugal force, and then cooled by liquid nitrogen to solidify it into powders. The microcrystalline powders manufactured by the process have very fine texture and small segregation with low cost, and can be easily produced in industrial scale. In the present invention, centrifugal atomization technique is used, for the first time, in the manufacture of ceramic hollow microspheres. Aqueous or non-aqueous slurries having certain characteristics (highly-stable foams having a certain solid phase content) are prepared, the foam slurries are atomized by centrifugal atomization to form hollow slurry droplets, the hollow slurry droplets are dried rapidly to obtain ceramic hollow microspheres. This is the first time that this technique is successfully used in ceramic systems and solid wastes containing inorganic non-metallic materials, broadening the application scopes and application prospects of hollow microspheres, and providing new approach to recycle solid wastes. At the meantime, this technique is also successfully used in the preparation of hollow microspheres of metals and alloy materials.
The process and device are versatile to ceramic powders of various material systems and can be used for the production of hollow microspheres of various ceramic materials (e.g., Al2O3, ZrO2, Si3N4, SiC etc.), solid wastes containing inorganic non-metallic materials (e.g., coal gangue, fly ash), and various metal and alloy material systems (e.g., WC, Ni, etc.). The hollow microspheres have a diameter of 0.001-1.5 mm, including closed-cell hollow microspheres and open-cell hollow microspheres. The open-cell or closed-cell hollow microspheres of this material system having a diameter of 0.001-1.5 mm have not been reported.